1. Field of the Invention
The present invention is utilized in a mobile phone service in an area covered by a plurality of different communication systems in mixed state. The present invention is commonly utilized in a plurality of different areas covered by different communication systems.
2. Description of Related Art
In an area covered by different communication systems providing respective mobile phone services, it is possible to improve a convenience of a user of a mobile phone by making the mobile terminal possible to correspond to a plurality of communication systems.
Alternatively, in a case where a user of a mobile phone reciprocates between a plurality of areas covered by different communication systems, a convenience of the user can be improved by corresponding the mobile phone to the respective communication systems.
In Japan, for example, a composite type mobile phone capable of operating in PDC (Personal Digital Cellular) mobile phone system or PHS (Personal Handy-phone System) selectively has been used. The composite type mobile phone includes a plurality of circuits corresponding to different communication systems, respectively, and operates by selecting one of the circuits.
The selection of circuit is manually performed by a user or automatically performed by the mobile phone itself. In the case of the automatic selection, the mobile phone determines one of the communication systems, which is employed in an area in which the mobile phone exists, and automatically selects one of the circuits.
Further, there is a composite type mobile phone capable of corresponding to the communication systems used in both Japan and other countries.
When a communication system is automatically selected by such conventional composite type mobile phone, there is no problem if a user of the mobile phone is in an area covered by any of the communication systems and the communication system covering the area is selected. However, when the user is out of areas covered by these communication systems, there is a problem in view of battery saving. That is, in such case, it is necessary for the mobile phone to repeatedly search base stations of all communication systems, so that a battery life of the mobile phone is shortened.
On the other hand, in a case where there is difference in charging system between communication systems, there may be a case where a communication system, which is not requested by a user, is automatically selected and the user is charged by an amount exceeding his expectation.
In the case where a communication system is manually selected by a user, there may be a case where the user can not accept a mobile phone service if he forgets a communication system he wants to use or he erroneously selects a wrong communication system.
Further, the manual operation for selecting the communication system is generally not easy. This is because, in order to avoid an interruption of communication when a communication system in use is switched to another by erroneous operations of buttons and/or switches of a mobile phone by a user during the communication, the selecting operation of communication system must be performed through a plurality of steps. When a user forgets the communication selecting operation requiring a plurality of steps, the user must re-confirm a manual, which is troublesome. That is, it is very troublesome for the user to check a communication system corresponding to his location and manually switch a communication system in use to another.